1. Field of the Invention
The present invention is directed to a hermetically welded and sealed oxygen cylinder assembly and more particularly, to a stored oxygen system that can release pure oxygen to aircraft crew and passengers with an extended life period that does not require frequent verification of status when installed in an aircraft.
2. Description of Related Art
Modern aircraft that fly passengers above 15,000 feet are required to meet certain standards as defined, for example, in the NASA/CR-2001-210903 “Onboard Inner Gas Generation System/Onboard Oxygen Gas Generation System Study, Part 1, Aircraft System Requirements,” May 2001.
Current passenger aircraft are required to be equipped with an emergency breathing system to provide oxygen should there be a failure of the primary pressurization system in the aircraft cabin. Thus, emergency breathing oxygen is made available to both crew and passengers, and is required to be operable for a sufficient period of time to enable a descent of the aircraft down to 10,000 feet. The passenger oxygen system is not designed to protect from smoke and toxic fumes, as required for the crew, but only against hypoxia.
The oxygen system for the crew members is separate from that of the passengers and further require sufficient oxygen to provide 15 minutes of breathing per crew member of oxygen at a cabin pressure altitude of 8,000 feet. Thus, for each crew member, 300 liters of the oxygen must be provided as a minimum and if the supply of oxygen falls below this minimum level, the pilot is required to reassess the flight plan and take appropriate action for the further operation of the aircraft, as required by the FAA and Joint Aviation Authorities (JAA).
Conventionally there have been two types of passenger oxygen systems that have been utilized in commercial jet transportation, namely chemical generation systems and stored gaseous systems. The chemical generation system has oxygen stored in the form of chemicals that are inside a metal container such as an oxygen chemical generator that can be stored above the passengers. When a chemical reaction is initiated upon an activation of a firing mechanism, such as pulling of the mask by a user, a pyrotechnic emission of the chemicals inside of the oxygen generator is created and 99.5% pure oxygen can be released.
Alternatively, for supplementing a chemical generation system, a gaseous oxygen system which utilizes pressurized cylinders such as 3,200 liter cylinders can be maintained at 1,850 PSI. An advantage of the gaseous oxygen system is the flexibility in adding additional cylinders to accommodate different flight profiles by extending an aircraft's capabilities by adjusting the number of oxygen cylinders. For example, a 777-300 aircraft would require 11 bottles of oxygen for just the passengers. The oxygen is stored in large pressure cylinders and is piped into various sections of the aircraft and, in an emergency, is actuated from the cockpit or automatically actuated by pressurization changes. The oxygen will flow from a valve on each of the pressurized cylinders to a regulator assembly where the pressure is reduced and subsequently flows into the individual mask for each passenger. The FAA/JAA requires the passenger oxygen system to be operative before the aircraft cabin's altitude exceeds 15,000 feet and be capable of releasing the required amount of oxygen in less than 10 seconds.
The current aircraft such as the Boeing 747, 767 and 777 and the Airbus A300, 320, 330 and 340 generally store their oxygen in large oxygen pressure cylinders, that are approximately 18 to 200 cubic inches in volume and are maintained at a normal pressure of approximately 1800 PSIG. These oxygen pressure cylinders have a Department of Transportation classification of DOT 3HT which require re-hydro tests and recharging every three years by the airline.
In addition, most of these emergency oxygen systems employ a valve sealing a main oxygen cylinder pressure with an elastomeric or metal crush seal washer that are not hermetically welded sealed. Generally the cylinder and the valve cannot be separated in prior art systems.
Thus, a substantial economic issue is involved in the removal and replacement in commercial aircraft of mounted oxygen pressure cylinders for re-hydro testing and recharging every three years. Additionally, a large number of spare cylinders are required to support this function by each of the individual aircraft operators at locations on a worldwide basis. This involves higher inventory cost along with the expensive man hours required to perform the retesting. Another major economic issue is the transportation of the cylinders removed from the aircraft to the retest and recharge facility.
It is further contemplated that proposed newer generation aircraft, such as the Boeing 787 and the Airbus A350, are planning to use smaller cylinders for oxygen storage and will be charged to a higher pressure to accommodate greater volume of oxygen in smaller cylinder volumes. Such newer cylinders are contemplated to be under a DOT classification of DOT 39. This specification permits oxygen cylinders to remain onboard the aircraft for long periods of time, provided they can safely maintain their oxygen charge. These pressurized cylinders cannot be recharged or reserviced.
The current common types of oxygen cylinders are composed of aluminum lined with carbon or Kevlar fibers on their outside. The internal wetted surfaces of the oxygen cylinders are coated with a type of polymer resin to protect against the effects of high pressure oxygen. An alternative commonly used oxygen cylinder is made from a 4130 carbon steel. Such cylinders have to be protected externally with an epoxy paint and also internally with a zinc phosphate plating. These types of internal coatings can be subject to cracking and chipping over an extended period of time, due to the constant pressure changes caused by temperature changes with corresponding expansions and contractions that can occur over the life of the aircraft. The resulting loose particulate material that may accumulate within the oxygen cylinder is a potential source of ignition during a cylinder content discharge as a result of the friction heat caused by high rate particle impacts. Since relatively pure oxygen is well known to be conducive to a fire in an appropriate environment, there is a need to provide an improved oxygen pressure cylinder that can take advantage of the extended life permitted under the DOT 39 classification.